Vibration suppression via piezoelectric shunt circuits has been of popular interest in recent years due to lightweight, ease of use, and good performance. Among the shunt devices that have been widely used are the resistive and inductive shunt circuits. However, these devices have, so far, been limited to control of a single vibration mode by matching the electrical resonance of the shunting device with the mechanical resonance of the vibrating structure or system.
The external terminals of a piezoelectric material, modeled as a capacitor (since, its electrical property is dominantly capacitance) are connected to the shunt branch circuit. The piezoelectric element is used to convert mechanical energy of the vibrating structure or system to electrical energy by direct piezoelectric effect. The electric energy is dissipated as heat through the shunt resistor efficiently when the electrical resonant frequency matches the targeted mechanical resonant frequency.
Many efforts have been made to develop a multi-mode structural vibration control device using inductive shunt circuit. For example, a theory was developed for suppressing multiple vibration modes by using a single piezoelectric material coupled with a multi-mode shunt network. Another example is a blocking circuit for filtering unwanted current frequencies. However, the conventional multi-mode vibration damper using a shunt circuit has a drawback in that it only provides damping of vibration in the limited frequency range.
A common factor in nature between a negative capacitance shunt circuit and an inductive resonant shunt circuit is that they have the same phase angle (90°). The magnitude of a negative capacitance in a negative capacitance shunt circuit should be equal or near as that of an inherent capacitance of piezoelectric material. Therefore, the negative capacitance circuit provides a negative capacitance of a magnitude that cancels the internal capacitance of a piezoelectric material in order to produce the maximum vibration damping capability.
Applying the above facts, a new multiple-mode vibration damper is invented by using negative capacitance shunting; one is connected two terminals of piezoelectric material to a resistor-negative capacitor shunt branch circuit in series, the other is connected with it in parallel. A piezo patch attached on the vibrating structure or system with a series resistor-negative capacitance shunting is designed to control the vibration and/or noise amplitudes in the low frequency range. The other patch bonded below the vibrating structure or system with a parallel resistor-negative capacitance shunting is for suppressing vibration modes in the high frequency range.